Transparent conductive film and production method therefor

ABSTRACT

The transparent conductive film of the invention includes a transparent conductive coating provided on at least one surface of an organic polymer film substrate, wherein the transparent conductive coating is a crystalline coating of an indium-based complex oxide having a tetravalent metal oxide content of 7 to 15% by weight as calculated by the formula {(the amount of the tetravalent metal element oxide)/(the amount of the tetravalent metal element oxide+the amount of indium oxide)}×100 (%), has a thickness of 10 to 40 nm and a specific resistance of 1.3×10 −4  to 2.8×10 −4  Ω·cm, has main X-ray diffraction peaks corresponding to (222) and (440) planes, and has a ratio (I 440 /I 222 ) of (440) peak intensity to (222) peak intensity of less than 0.2. The transparent conductive film of the invention has a crystalline thin coating with a low level of specific resistance and surface resistance.

TECHNICAL FIELD

The invention relates to a transparent conductive film having hightransparency in the visible light region and including an organicpolymer film substrate and a transparent conductive coating providedthereon. The invention also relates to a method for producing thetransparent conductive film. The transparent conductive film of theinvention has a transparent conductive thin coating with a low level ofspecific resistance and surface resistance.

The transparent conductive film of the invention is useful for electrodeapplications requiring low surface resistance, such as transparentelectrodes for displays such as film liquid crystal displays and filmOLED displays, transparent electrodes for capacitive touch panels, andelectrodes for film OLED lighting. The transparent conductive film ofthe invention is also suitable for use as a film solar cell electrodeand for use in the prevention of static charge of transparent products,the shielding of electromagnetic waves from transparent products, andother applications.

BACKGROUND ART

A conventionally well-known transparent conductive film is what iscalled a conductive glass, which includes a glass substrate and an ITOcoating (indium-tin complex oxide coating) formed thereon. When an ITOcoating is formed on a glass substrate, the coating can be depositedwhile the glass substrate is heated at 200° C. or higher, generally,300° C. or higher. In this case, therefore, an ITO coating with athickness of 130 nm and a low surface resistance of 10 Ω/square or less(a specific resistance of 1.3×10⁻⁴ Ω·cm) can be easily obtained.

However, the glass substrate, which has low flexibility and workability,cannot be used in some cases. In recent years, therefore, transparentconductive films having an ITO coating formed on various organic polymerfilm substrates such as polyethylene terephthalate films are usedbecause of their advantages such as a high level of flexibility,workability, and impact resistance, and light weight.

The preferred level of specific resistance and surface resistance,required of the ITO coating-bearing transparent conductive film, varieswith the use of the transparent conductive film. However, the ITOcoating formed on the organic polymer film substrate has become requiredto have the same level of specific resistance and surface resistance asthat of the ITO coating formed on the glass substrate. For example, filmdisplays have been studied recently. For such display applications, theITO coating formed on the organic polymer film substrate has beenrequired to have a low resistance of 10 Ω/square or less per 130 nmthickness, which is the same level as that of the ITO coating formed onthe glass substrate. An ITO coating for use in capacitive touch panelelectrode applications, which is patterned into an antenna structure, isalso required to have a surface resistance as low as about 100 Ω/square.In addition, such an ITO coating for use in capacitive touch panelelectrode applications is required to have a low surface resistance evenwhen having a thickness of about 20 nm because there must be nodifference in reflection color between the etched and non-etched parts.Thus, ITO coatings for use in capacitive touch panel electrodeapplications are required to have a low level of specific resistanceclose to that for display applications.

A variety of processes are proposed for the ITO coating-bearingtransparent conductive film (Patent Documents 1 to 4).

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2010-177161

Patent Document 2: JP-A-02-232358

Patent Document 3: JP-A-03-249171

Patent Document 4: JP-A-2011-018623

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Unfortunately, an ITO coating deposited on an organic polymer filmsubstrate generally has a specific resistance higher than that of an ITOcoating deposited on a glass substrate. There may be two reasons forthis. A first reason is that most organic polymer film substrates cannotbe heated at high temperatures because their glass transitiontemperature or heat-resistant temperature is lower than 200° C., and,therefore, the amount of tin atoms substituting for indium sites islimited so that the resulting ITO coating has an electron carrierdensity n lower by one order of magnitude. A second reason is that wateradsorbed on an organic polymer film substrate and gases generated whenthe substrate is brought into contact with plasma, as well as excess tinatoms contained in a target, can act as impurities to inhibit crystalgrowth. Thermal deformation and low smoothness of a film substrate mayalso have an adverse effect on crystal growth. Excess tin atoms are morelikely to be locally converted to tin oxide (SnO₂), which can not onlyinhibit crystal growth but also form defects capable of scatteringelectrons also into crystals. Both causes are considered to worktogether to reduce electron mobility μ. For these reasons, it has beendifficult to form an ITO coating with a thickness of 130 nm, a surfaceresistance of about 30 Ω/square, and a specific resistance of 4×10⁻⁴Ω·cm or less on an organic polymer film substrate. Also, ITO coatingsfor use in capacitive touch panel electrode applications are required tohave a thickness of around 20 nm. However, when an ITO coating with sucha thickness is formed on an organic polymer film substrate, the ITOcoating is difficult to crystallize due to the effect of impurities fromthe substrate and the like, so that it is difficult to obtain a specificresistance as good as that of a thick coating.

Patent Document 1 proposes that an ITO coating having a strongest X-raydiffraction peak corresponding to the (400) plane and having a specificresistance (volume resistance) of 1×10⁻⁴ to 6×10⁻⁴ Ω·cm can be depositedby using plasma assisted sputtering in which plasma is generated at amiddle position between a substrate and a target during the sputteringor by using ion beam assisted sputtering in which sputtering isperformed with ion beam assistance. However, this method has a problemwith uniformity or stability in a roll-to-roll (R-to-R) system althoughthe ion beam or additional RF plasma can be used between a target (T)and a substrate (S) when a batch deposition system with a narrow T-Sdistance is used for sputtering deposition. Patent Document 1 shows thatthe resulting ITO coating has a carrier concentration of 5×10²⁰ to2×10²¹ cm⁻³ and a carrier mobility of 15 to 25 cm²/V/s and that the ITOcoating in the examples has a thickness of 200 nm and a volumeresistance of about 5×10⁻⁴ Ω·cm. The disclosure in Patent Document 1does not make it possible to obtain a 10 to 40-nm-thick ITO thin coatingwith a substantially low specific resistance of 1×10⁻⁴ Ω·cm.

Patent Documents 2 and 3 propose that in magnetron sputteringdeposition, recoiling argon- or oxygen negative ions-induced damage tothe deposited coating can be reduced by increasing the magnetic fieldintensity or by superimposing RF power to reduce the discharge voltage,so that an ITO coating with a low specific resistance can be deposited.Patent Documents 2 and 3 disclose the use of a glass substrate, whichcan be heated at high temperatures. However, when an organic polymerfilm substrate is used in the method described in Patent Documents 2 and3, the substrate can be heated only to the glass transition temperatureor lower. Therefore, if an organic polymer substrate film is used in themethod described in Patent Documents 2 and 3, the resulting ITO coatingis an amorphous coating. Even if the technique described in PatentDocuments 2 and 3 is used, it is not possible to form, on an organicpolymer film substrate, a completely crystallized ITO coating with aspecific resistance as low as that of an ITO coating formed on a glasssubstrate. In addition, the examples in Patent Documents 2 and 3 onlyshow that the resulting coating has a thickness of 100 nm, which doesnot suggest any study of thin coatings with a thickness of 10 to 40 nm.

Patent Document 4 proposes an ITO coating deposition method in which anRF power of 0.5 to 2.0 times DC power is superimposed in a targetsurface magnetic field of 60 to 80 mT. The document discloses that theITO coating obtained by the deposition method can have a low resistivity(specific resistance) of 1.5×10⁻⁴ Ω·cm or less when the coating forms aspecific crystalline state in which the (400) plane peak is greater thanthe (222) plane peak, as measured by X-ray diffraction method. However,Patent Document 4 shows the use of a glass substrate, which can be setin the temperature range of 230 to 250° C. If an organic polymer filmsubstrate is used in the method described in Patent Document 4, it isdifficult to obtain the (400) plane peak as a main peak, which meansthat in that case, it is not possible to deposit an ITO coating with aspecific resistance as low as that shown in Patent Document 4.

It is an object of the invention to provide a transparent conductivefilm including an organic polymer film substrate and a transparentconductive coating that is provided on the substrate and made of acrystalline thin coating and has a low level of specific resistance andsurface resistance, and to provide a method for producing such atransparent conductive film.

Means for Solving the Problems

As a result of earnest study to achieve the object, the inventors haveaccomplished the invention based on findings that the object can beachieved by the transparent conductive film and the method forproduction thereof described below.

Specifically, the invention is directed to a transparent conductivefilm, including: an organic polymer film substrate; and a transparentconductive coating provided on at least one surface of the organicpolymer film substrate, wherein

the transparent conductive coating is a crystalline coating of anindium-based complex oxide having a content of a tetravalent metalelement oxide of 7 to 15% by weight as calculated by the formula {(theamount of the tetravalent metal element oxide)/(the amount of thetetravalent metal element oxide+the amount of indium oxide)}×100(%),

the transparent conductive coating has a thickness in the range of 10 nmto 40 nm,

the transparent conductive coating has a specific resistance of 1.3×10⁻⁴to 2.8×10⁻⁴ Ω·cm, and

the transparent conductive coating has main X-ray diffraction peakscorresponding to (222) and (440) planes and also has a ratio (I₄₄₀/I₂₂₂)of (440) peak intensity (I₄₄₀) to (222) peak intensity (I₂₂₂) of lessthan 0.2.

The transparent conductive film may further include an undercoat layerprovided on the film substrate, wherein the transparent conductivecoating may be provided on the film substrate with the undercoat layerinterposed therebetween.

In the transparent conductive film, the indium-based complex oxide maybe an indium-tin complex oxide, and the tetravalent metal element oxidemay be tin oxide.

The invention is also directed to a method for producing the transparentconductive film, the method including:

the step (A) of forming a transparent conductive coating on at least onesurface of an organic polymer film substrate in the presence of inertgas by RF superimposed DC sputtering deposition using an indium-basedcomplex oxide target with a high horizontal magnetic field of 85 to 200mT at the surface of the target, wherein the indium-based complex oxidetarget has a content of a tetravalent metal element oxide of 7 to 15% byweight as calculated by the formula {(the amount of the tetravalentmetal element oxide)/(the amount of the tetravalent metal elementoxide+the amount of indium oxide)}×100(%).

In the transparent conductive film-producing method, the high magneticfield RF superimposed DC sputtering deposition in the forming step (A)is preferably performed with a ratio of RF power to DC power of 0.4 to1.2 when the RF power source has a frequency of 10 to 20 MHz.

In the transparent conductive film-producing method, the high magneticfield RF superimposed DC sputtering deposition in the forming step (A)is preferably performed with a ratio of RF power to DC power of 0.2 to0.6 when the RF power source has a frequency of more than 20 MHz to 60MHz.

In the transparent conductive film-producing method, the organic polymerfilm substrate preferably has a temperature of 80 to 180° C. in the highmagnetic field RF superimposed DC sputtering deposition in the formingstep (A).

In the transparent conductive film-producing method, the high magneticfield RF superimposed DC sputtering deposition in the forming step (A)may be performed without introducing oxygen.

In the transparent conductive film-producing method, the high magneticfield RF superimposed DC sputtering deposition in the forming step (A)may be performed while oxygen is introduced in such a way that theamount of oxygen is 0.5% or less relative to the amount of the inertgas.

The transparent conductive film-producing method may further include apre-sputtering step (a) that is performed before the high magnetic fieldRF superimposed DC sputtering deposition and includes forming a coatingin the presence of inert gas without introduction of oxygen by RFsuperimposed DC sputtering deposition with a ratio of RF power to DCpower of 0.4 to 1.2 at an RF power source frequency of 10 to 20 MHzuntil the resulting resistance reaches a stable level.

The transparent conductive film-producing method may further include apre-sputtering step (a) that is performed before the high magnetic fieldRF superimposed DC sputtering deposition and includes forming a coatingin the presence of inert gas without introduction of oxygen by RFsuperimposed DC sputtering deposition with a ratio of RF power to DCpower of 0.2 to 0.6 at an RF power source frequency of more than 20 MHzto 60 MHz until the resulting resistance reaches a stable level.

The transparent conductive film-producing method may further include anannealing step (B) that is performed after the forming step (A). Theannealing step (B) is preferably performed at a temperature of 120 to180° C. for 5 minutes to 5 hours in the air.

Effect of the Invention

The invention makes it possible to provide a transparent conductive filmincluding an organic polymer film substrate and a crystallinetransparent conductive coating that is provided on the substrate andmade of a thin coating (20 to 40 nm) of an indium-based complex oxide(such as an indium-tin complex oxide (ITO)) and has the same low levelof specific resistance and surface resistance as a transparentconductive coating formed on a glass substrate.

According to the transparent conductive film-producing method of theinvention, a crystalline transparent conductive thin coating having thesame low level of specific resistance and surface resistance as atransparent conductive coating formed on a glass substrate can bedeposited on an organic polymer film substrate using a roll-to-roll(R-to-R) system under temperature conditions lower than those forforming a transparent conductive coating on a glass substrate.

According to the production method of the invention, the high magneticfield RF superimposed DC sputtering deposition can be adapted tomanufacturing facility, in which the RF power can be set smaller thanthe DC power, and the RF power-introducing process and radio waveshielding can be easily performed in the high magnetic field RFsuperimposed DC sputtering deposition. In addition, even when anamorphous transparent conductive coating is formed by the high magneticfield RF superimposed DC sputtering deposition in the forming step (A),the transparent conductive coating can be crystallized by a heattreatment at a low temperature for a short time in the annealing step(B), so that the resulting transparent conductive coating has a hightransmittance and high reliability.

In the production method of the invention, the pre-sputtering step (a),which has been previously unknown, may be performed before the highmagnetic field RF superimposed DC sputtering deposition for the formingstep (A). In this case, not only water can be removed from the surfaceof the indium-based complex oxide target, but also modification can beperformed so that oxygen in the target itself can be ready to beefficiently incorporated into the ITO crystal coating, which makes itpossible to efficiently obtain a transparent conductive coating with alow content of defects and impurities and a low level of specificresistance and surface resistance under temperature conditions lowerthan those for forming a transparent conductive coating on a glasssubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of thetransparent conductive film of the invention;

FIG. 2 is a schematic diagram showing an example of a system for use inhigh magnetic field RF superimposed DC sputtering deposition for thetransparent conductive film-producing method of the invention;

FIG. 3 is a graph showing frequency-dependent changes in dischargevoltage in the high magnetic field RF superimposed DC sputteringdeposition according to the invention;

FIG. 4 is a graph showing the relationship between the discharge voltageand the resistance in a case where conventional high magnetic field RFsuperimposed DC sputtering deposition is reexamined;

FIG. 5 is a graph showing the relationship between the optimal oxygensupply and the resistance in a case where conventional high magneticfield RF superimposed DC sputtering deposition is reexamined;

FIG. 6 is a graph showing an advantageous effect obtained whenpre-sputtering is performed before the high magnetic field RFsuperimposed DC sputtering deposition in the production method of theinvention;

FIG. 7 is a graph showing the effect of the ratio of RF power to DCpower in a case where RF power is provided at 13.56 MHz in the highmagnetic field RF superimposed DC sputtering deposition according to theinvention;

FIG. 8 is a graph showing the effect of the ratio of RF power to DCpower in a case where RF power is provided at 27.12 MHz in the highmagnetic field RF superimposed DC sputtering deposition according to theinvention;

FIG. 9 is a graph showing the effect of the ratio of RF power to DCpower in a case where RF is 40.68 MHz in the high magnetic field RFsuperimposed DC sputtering deposition according to the invention;

FIG. 10 is a graph showing the effect of the ratio of RF power to DCpower in a case where RF is 54.24 MHz in the high magnetic field RFsuperimposed DC sputtering deposition according to the invention;

FIG. 11 is a grazing incidence X-ray diffraction chart of an ITO filmobtained in Example 1 according to the invention; and

FIG. 12 is a TEM photograph showing crystals in an ITO film obtained inExample 5 according to the invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the transparent conductive film of the invention and themethod for the production thereof will be described with reference tothe drawings. FIG. 1 is a schematic cross-sectional view showing anexample of the transparent conductive film of the invention, whichincludes an organic polymer film substrate (1) and a transparentconductive coating (2) provided on one surface of the substrate (1). Thetransparent conductive coating (2) is made of an indium-based complexoxide containing an oxide of a tetravalent metal element. Although FIG.1 shows that the transparent conductive coating (2) is provided on onlyone surface of the organic polymer film substrate (1), the transparentconductive coating (2) may also be provided on the other surface of thefilm substrate (1).

Although not shown in FIG. 1, an undercoat layer for anti-reflection orother purposes may be provided on the film substrate (1), and thetransparent conductive coating (2) may be provided on the film substrate(1) with the undercoat layer interposed therebetween. When a transparentconductive thin coating (2) is formed by high magnetic field RFsuperimposed DC sputtering deposition as in the production method of theinvention, elements such as C and H can be incorporated from the organicpolymer film substrate (1) into an ITO coating to make thecrystallization of the coating difficult. In this case, therefore, it ispreferable to form the undercoat layer.

A film with a high level of transparency, heat resistance, and surfacesmoothness is preferably used as the organic polymer film substrate (1).Examples of the material for such a film include polyester such aspolyethylene terephthalate or polyethylene naphthalate, polyolefin,polycarbonate, polyether sulfone, polyarylate, polyimide, polyamide,polystyrene, and homopolymers or copolymers of norbornene or the like.The organic polymer film substrate (1) may also be an epoxy resin filmor the like.

In general, the thickness of the film substrate (1) is preferably in therange of 16 to 400 μm, more preferably in the range of 20 to 185 μm,although it depends on the deposition conditions or intended use. Thecoating may be formed on the film being taken up in a roll-to-roll(R-to-R) system. In this case, if the film is too thin, heat-inducedwrinkles or static electricity can occur to make the take-up processdifficult, and if the film is too thick, the film can behave like asolid plate and be impossible to take up.

The film substrate (1) may be subjected to a surface modification step(pretreatment) depending on the type of the film substrate (1). Thesurface modification treatment may be a plasma treatment under an inertgas atmosphere such as an argon or nitrogen gas atmosphere.Alternatively, the film substrate (1) may be previously subjected tosputtering, corona discharge, flame treatment, ultraviolet irradiation,electron beam irradiation, chemical treatment, oxidation, or otheretching or undercoating treatment so that it can have improved tackinessto the transparent conductive coating (2) or the undercoat layer formedthereon. If necessary, dust removing or cleaning may also be performedon the film substrate (1) by solvent or ultrasonic cleaning before thetransparent conductive coating (2) or the undercoat layer is formed.

The undercoat layer may be made of an inorganic material, an organicmaterial, or a mixture of inorganic and organic materials. The inorganicmaterial is preferably, for example, SiO_(x) (x=1 to 2), MgF₂, Al₂O₂,TiO₂, Nb₂O₅, or the like. The organic material may be an acrylic resin,a urethane resin, a melamine resin, an alkyd resin, a siloxane polymer,or the like. The organic material is preferably a thermosetting resinincluding a blend of a melamine resin, an alkyd resin, and anorganosilane condensate.

Using any of the above materials, the undercoat layer can be formed by adry process such as vacuum deposition, sputtering, or ion plating or awet process (coating process) or the like. A single undercoat layer maybe provided, or two or more undercoat layers may be provided. Ingeneral, the thickness of the undercoat layer (or the thickness of eachof two or more undercoat layers) may be from about 1 to about 300 nm.

The material used to form the transparent conductive coating (2) may beappropriately selected depending on the method for forming the thincoating. In general, a sintered material composed of indium oxide and anoxide of a tetravalent metal element is preferably used to form thetransparent conductive coating (2).

Examples of the tetravalent metal element include tin, cerium, hafnium,zirconium, titanium, and the like. Oxides of these tetravalent metalelements include tin oxide, cerium oxide, hafnium oxide, zirconiumoxide, titanium oxide, and the like. Tin is preferably used as thetetravalent metal element. The oxide of the tetravalent metal element ispreferably an oxide of tin, and the indium-based complex oxide ispreferably an indium-tin complex oxide.

The transparent conductive coating (2) is formed using an indium-basedcomplex oxide including indium oxide and a tetravalent metal elementoxide, in which the content of the tetravalent metal element oxidecalculated by the formula {(the amount of the tetravalent metal elementoxide)/(the amount of the tetravalent metal element oxide+the amount ofindium oxide)}×100(%) is from 7 to 15% by weight. The content of thetetravalent metal element oxide in the indium-based complex oxide ispreferably from 8 to 13% by weight.

If the content of the tetravalent metal element oxide in theindium-based complex oxide is low, the amount of the tetravalent metalatoms capable of replacing the indium atoms will be relatively small,which can make it difficult to ensure a sufficient electron density andto obtain a transparent conductive coating with a low resistance. On theother hand, if the content is high, not only it will be difficult tocrystallize the resulting transparent conductive coating (amorphouscoating), but also a surplus amount of the tetravalent metal element orthe oxide may remain to form an impurity region, so that the resultingtransparent conductive coating may have degraded properties, because thetemperature which the polymer film substrate (1) can withstand isgenerally around 180° C. or less and therefore the substitution of theindium lattice with the tetravalent metal atoms is limited.

The thickness of the transparent conductive coating (2), whichinfluences the increase of application size or the improvement ofconduction efficiency, is from 10 to 40 nm, preferably from 15 to 35 nm,more preferably from 20 to 30 nm, in view of optical properties,resistance, or the like. The transparent conductive coating (2) with athickness of 10 to 40 nm is suitable for electrode applications fortouch panels and the like.

The transparent conductive coating (2) is a crystalline coating.Preferably, the crystalline coating is completely crystallized. Whetherit is a crystalline coating can be determined by transmission electronmicroscope (TEM) observation. As used herein, the term “completelycrystallized” refers to the state in which crystallized grains arepresent over the entire surface observed with a transmission electronmicroscope (TEM). On the other hand, the transparent conductive coatingdecreases in surface resistance as crystallization proceeds, and itssurface resistance becomes constant when crystallization is completed.Therefore, whether it is a crystalline coating can be determined by thefact that its surface resistance becomes constant. The transparentconductive coating preferably has a surface resistance of 100 Ω/squareor less, more preferably 70 Ω/square or less.

The transparent conductive coating (2) has a low specific resistance of1.3×10⁻⁴ to 2.8×10⁻⁴ Ω·cm. The specific resistance is preferably from1.3×10⁻⁴ to 2.0×10⁻⁴ Ω·cm, more preferably from 1.3×10⁻⁴ to 1.8×10⁻⁴Ω·cm.

The transparent conductive coating (2) has main X-ray diffraction peakscorresponding to (222) and (440) planes and also has a ratio (I₄₄₀/I₂₂₂)of the (440) peak intensity (I₄₄₀) to the (222) peak intensity (I₂₂₂) ofless than 0.2. The main X-ray diffraction peak corresponding to the(222) plane is the most intense peak, which indicates a coatingcrystallized at low temperature. When the peak intensity ratio(I₄₄₀/I₂₂₂) is less than 0.2, the coating is not polycrystalline andthus has high mobility and high near-infrared transmittance and is nothigh in electron density, which provides high reliability against heatand moisture and therefore is preferred. The peak intensity ratio(I₄₄₀/I₂₂₂) is preferably 0.19 or less, more preferably 0.18 or less.

Next, the method of the invention for producing the transparentconductive film will be described. The method of the invention forproducing the transparent conductive film includes the step (A) offorming a transparent conductive coating in the presence of inert gas byRF superimposed DC sputtering deposition using an indium-based complexoxide target with a high horizontal magnetic field of 85 to 200 mT atthe surface of the target.

FIG. 2 is a schematic diagram showing an example of a deposition systemfor use in high magnetic field RF superimposed DC sputtering depositionfor the forming step (1). FIG. 2 shows a sputtering system in which anindium-based complex oxide target (2A) is attached to a sputteringelectrode (3) and used to form an indium-based complex oxide thincoating (2) on a film substrate (1) facing the target (2A). The filmsubstrate (1) is held on a substrate holder or can roll (1A). Thehorizontal magnetic field on the target (2A) is set at 85 to 200 mT,which is higher than a normal magnetic field (30 mT). Such a highmagnetic field can be adjusted by providing high-field magnets (4).Setting the magnetic field high makes it possible to obtain atransparent conductive coating having a low level of specific resistanceand surface resistance. The high magnetic field is preferably from 100to 160 mT.

In general sputtering deposition, a DC power source (direct currentsource) (8) is used to apply DC power or pulsed power to a target whensputtering is performed. As shown in the system of FIG. 2, however, thehigh magnetic field RF superimposed DC sputtering deposition accordingto the invention is performed using a DC power source (8) and an RFpower source (7) (a variable frequency, high-frequency power source).The RF power source (7) and the DC power source (8) are so arranged andconnected to the sputtering electrode (3) as to apply RF power and DCpower at the same time. As shown in FIG. 2, a matching box (5) may beprovided between the RF power source (7) and the sputtering electrode(3) to efficiently transmit RF power from the RF power source (7) to thetarget (2A). As shown in FIG. 2, a water cooled low-pass filter (6) mayalso be placed between the DC power source (8) and the sputteringelectrode (3) so that the RF power from the RF power source (7) will nothave any effect on the DC power source (8).

In the high magnetic field RF superimposed DC sputtering deposition forthe forming step (A), when the frequency of the RF power source is from10 to 20 MHz, the ratio of the RF power to the DC power is preferablyset to 0.4 to 1.2 in view of low-damage deposition and the degree ofoxidation of the coating. The power ratio is preferably from 0.5 to 1.0,more preferably from 0.6 to 1.0. The RF power source frequency (10 to 20MHz) is preferably 13.56 MHz. On the other hand, when the frequency ofthe RF power source is higher than 20 MHz and not higher than 60 MHz,the ratio of the RF power to the DC power is preferably set to 0.2 to0.6 in view of low-damage deposition and the degree of oxidation of thecoating. In this case, the power ratio is preferably from 0.3 to 0.5.The RF power source frequency (higher than 20 MHz and not higher than 60MHz) is preferably 27.12 MHz, 40.68 MHz, or 54.24 MHz.

In the high magnetic field RF superimposed DC sputtering deposition forthe forming step (A), the temperature of the organic polymer filmsubstrate (1) is preferably from 80 to 180° C. When the temperature ofthe film substrate (1) is 80° C. or higher during the sputteringdeposition, a seed for crystallization can be formed even in anindium-based complex oxide coating with a high tetravalent metal atomcontent. When the transparent conductive coating formed in the step (A)is amorphous, the annealing step (B) described below can easilyfacilitate the crystallization of the indium-based complex oxidecoating, so that a crystalline transparent conductive coating (2) with alower surface resistance can be obtained. Therefore, the temperature ofthe film substrate (1) is preferably 100° C. or higher, more preferably120° C. or higher, even more preferably 130° C. or higher, further morepreferably 140° C. or higher, so that the amorphous transparentconductive coating can be crystallized by heating to form a crystallinetransparent conductive coating (2) with a low surface resistance. Inorder to suppress thermal damage to the film substrate (1), thetemperature of the substrate is preferably 180° C. or lower, morepreferably 170° C. or lower, even more preferably 160° C. or lower.

As used herein, the term “the temperature of the film substrate” refersto the set temperature of the support on which the film substrate isplaced during the sputtering deposition. For example, when a rollsputtering system is used to perform continuous sputtering deposition,the temperature of the substrate corresponds to the temperature of thecan roll on which sputtering deposition is performed. When sputteringdeposition is performed piece by piece (batch mode), the temperature ofthe substrate corresponds to the temperature of the substrate holderadapted to hold the substrate.

The high magnetic field RF superimposed DC sputtering deposition for theforming step (A) may be performed as follows. The sputtering target isplaced in the sputtering system, which is then evacuated to high vacuum.Inert gas such as argon gas is then introduced into the sputteringsystem. The deposition may be performed without introducing oxygen intothe sputtering system containing inert gas such as argon gas. On theother hand, to improve the transmittance of the transparent conductivecoating, oxygen gas or the like may be introduced in addition to theinert gas such as the argon gas, when the transparent conductive coatingis desired as a crystalline coating immediately after the deposition inthe forming step (A), when the deposition is performed using a ratio ofthe RF power to the DC power of 0.4 to 0.6 at an RF power sourcefrequency of 10 to 20 MHz, or when the deposition is performed using aratio of the RF power to the DC power of 0.2 to 0.3 at an RF powersource frequency of more than 20 MHz to 60 MHz. Otherwise, anoxygen-deficient coating may be formed in these cases. The oxygen gas ispreferably so introduced that the amount of oxygen is 0.5% or less, morepreferably 0.3% or less, relative to the amount of the inert gas.

If water molecules are present in the deposition atmosphere, they canterminate dangling bonds, which occur during the deposition, andinterfere with the growth of an indium-based complex oxide crystal.Therefore, the deposition atmosphere preferably has a lower waterpartial pressure. During the deposition, the partial pressure of wateris preferably 0.1% or less, more preferably 0.07% or less of the partialpressure of the inert gas. During the deposition, the partial pressureof water is preferably 2×10⁻⁴ Pa or less, more preferably 1.5×10⁻⁴ Pa orless, even more preferably 1×10⁻⁴ Pa or less. In order to set thepartial pressure of water in the above range during the deposition, thesputtering system is preferably evacuated to 1.5×10⁻⁴ Pa or less, morepreferably 5×10⁻⁵ Pa or less, before the start of the deposition so thatwater and impurities such as organic gases generated from the substrateare removed from the atmosphere in the system and the partial pressureof water falls within the above range.

Particularly, when an R-to-R system is used for continuous production,the generated gases are preferably removed while the substrate is fedwithout performing deposition. Otherwise crystallization can bedifficult, particularly when a transparent conductive thin coatingincluding an indium-based complex oxide with a high content of atetravalent metal oxide (such as tin oxide) is obtained.

Before the high magnetic field RF superimposed DC sputtering depositionis performed for the forming step (A), a pre-sputtering step (a) may beperformed. The pre-sputtering step (a) includes performingpre-sputtering deposition in the presence of inert gas withoutintroduction of oxygen by RF superimposed DC sputtering deposition witha high horizontal magnetic field of 85 to 200 mT at the surface of thetarget with a ratio of RF power to DC power in the same range as one ofthe ranges for the main deposition step until the resulting resistancereaches a stable level.

The phrase “the resulting resistance reaches a stable level” indicatesthe phase ▴4▾ in FIG. 6, which means that phases in which water andgases generated on and from the target and the vacuum chamber wall areremoved (phases ▴1▾ to ▴3▾) go by, so that fluctuations in theresistance fall within ±2% as a result of stable activation of thetarget surface with the high magnetic field and the RF and DC powers.

An annealing step (B) may be performed after the transparent conductivethin coating is formed by the high magnetic field RF superimposed DCsputtering deposition in the forming step (A). When an amorphoustransparent conductive coating is formed in the step (A), the coatingcan be crystallized by the annealing step (B).

The annealing step (B) is preferably performed at a temperature of 120to 180° C. for 5 minutes to 5 hours in the air. When the heatingtemperature and the heating time are appropriately selected, the coatingcan be converted to a completely crystallized form without degradationof productivity or quality. The annealing may be performed by a knownmethod using a heating system such as an infrared heater or a hot aircirculation oven.

A crystalline coating of an indium-based complex oxide may be obtainedwithout the annealing step (B). In this case, the temperature of theorganic polymer film substrate (1) is preferably set at 150° C. orhigher in the above range in the high magnetic field RF superimposed DCsputtering deposition for the forming step (A). In this case, when theRF power source frequency is 10 to 20 MHz, the ratio of the RF power tothe DC power is preferably set at less than 1.2 in the above range. TheRF power source frequency (10 to 20 MHz) is preferably 13.56 MHz. Whenthe RF power source frequency is higher than 20 MHz and not higher than60 MHz, the ratio of the RF power to the DC power is preferably set atless than 0.6. The RF power source frequency (higher than 20 MHz and nothigher than 60 MHz) is preferably 27.12 MHz, 40.68 MHz, or 54.24 MHz.

The transparent conductive film may be used to form a projectivecapacitive touch panel, a matrix resistive touch panel, or the like. Inthis case, the resulting transparent conductive coating (2) may bepatterned into a predetermined shape (such as a strip shape). It shouldbe noted that after crystallized by the annealing step (B), anindium-based complex oxide coating can resist acid etching, whereasbefore the annealing step (B), an amorphous indium-based complex oxidecoating can be easily etched. Therefore, an amorphous transparentconductive coating (2) should be formed and then patterned by etchingbefore the annealing step (B).

The production method of the invention makes it possible to obtain acrystalline transparent conductive coating of an indium-based complexoxide having a thickness of 10 nm to 40 nm, the low specific resistancementioned above, and a peak intensity ratio (I₄₄₀/I₂₂₂) of less than0.2. When the transparent conductive coating is formed by high magneticfield RF superimposed DC sputtering deposition on the film substratebeing heated at a temperature of 80 to 180° C., the discharge voltagecan be reduced to ½ to ⅕ of that in a normal magnetic field depositionprocess. In this case, therefore, the kinetic energy of atoms andmolecules being deposited on the film substrate can be reducedcorrespondingly. In addition, negative ions such as electrons andrecoiling inert gas having collided with the target are also less likelyto reach the film substrate, so that the internal stress and thecontamination of the coating with impurities can be reduced. Inaddition, the deposition at a film substrate temperature of 80 to 180°C. can form a coating capable of undergoing facilitated (222)-orientedcrystal growth.

Hereinafter, conditions for the method of the invention for producingthe transparent conductive film will be further described with referenceto FIGS. 3 to 11.

Indium-based complex oxide targets (specifically, indium-tin complexoxide targets) available from Japanese manufacturers have remarkablyimproved quality. Every manufacturer has been able to provide the samelevel of product properties. All manufacturers' target products have arelative density of 98% or more and substantially the same degree ofoxidation. When a chamber is sufficiently pre-evacuated to 1.5×10⁻⁴ Paor less for general magnetron sputtering deposition with such products,a transparent conductive coating with a minimum surface resistance canbe obtained with oxygen introduced in an amount of about 1 to about 3%relative to the amount of the sputtering gas (inert gas) such as argongas.

An indium-tin complex oxide (ITO) target with a tin oxide content of 10%by weight was placed in the high magnetic field RF superimposed DCsputtering system of FIG. 2, in which an ITO coating was formed on a125-μm-thick PET film. The temperature of the film substrate was 120°C., the oxygen content was 0.25% based on the amount of argon gas, andthe deposition pressure was 0.3 Pa. FIG. 3 shows the results ofdischarge voltage measurement with different RF powers and different RFpower source frequencies at a certain DC power (1,000 W). The horizontalmagnetic field at the target surface was 100 mT. For all RF power sourcefrequencies, the discharge voltage decreases with increasing RF power,although the discharge voltage asymptotically approaches a constantvalue as the ratio of the RF power to the DC power approaches 1. Adifference can be seen between the discharge voltage decline curvesobtained when the RF power source frequency is 13.56 MHz and when the RFpower source frequency is 27.12 MHz, 40.68 MHz, or 54.24 MHz. Thedischarge voltage is lower when the RF power source frequency is 2, 3,or 4 times 13.56 MHz than when it is 13.56 MHz. This may be becausehigher frequencies have a higher ability to generate plasma.

Under the same conditions as those shown above (the RF frequency usedwas 13.56 MHz), a 28-nm-thick ITO coating was formed on a 125-μm-thickPET film by high magnetic field RF superimposed DC sputtering depositionat different discharge voltages. The resulting ITO coatings weremeasured for initial surface resistances (R₀). Subsequently, the ITOcoatings were annealed at 150° C. for 1 hour and then measured forsurface resistances (R_(150° C. 1 h)). FIG. 4 shows the results. It isapparent from FIG. 4 that the initial surface resistance (R₀) decreasedas decreasing discharge voltage and that the surface resistance(R_(150° C. 1 h)) was slightly reduced after the annealing. However, theminimum surface resistance and specific resistance of the resulting ITOcoating were 160 Ω/square and 4.5×10⁻⁴ Ω·cm, respectively. Therefore,the same properties as those of an ITO coating formed on a glasssubstrate (target values such as a low surface resistance of 100Ω/square or less and a specific resistance of 2.0×10⁻⁴ Ω·cm or less)were not obtained.

Under the same conditions as those shown above (the RF frequency usedwas 13.56 MHz), a 28-nm-thick ITO coating was also formed on a125-μm-thick PET film by high magnetic field RF superimposed DCsputtering deposition at a discharge voltage of 110 V (a ratio of RFpower to DC power of 1.0) with different contents of introduced oxygengas during ITO deposition. The resulting ITO coatings were measured forinitial surface resistances (R₀). Subsequently, the ITO coatings wereannealed at 150° C. for 1 hour and then measured for surface resistances(R_(150° C. 1 h)). FIG. 5 shows the results of examining whether a lowsurface resistance can be obtained by changing the amount of oxygenrelative to the amount of argon gas. The initial surface resistance (R₀)and the surface resistance (R_(150° C. 1 h)) after the annealing werefurther reduced by optimizing the amount of introduced oxygen gas, butthe minimum surface resistance and specific resistance of the resultingITO coating were 150 Ω/square and about 4.2×10⁻⁴ Ω·cm, respectively.

As shown in FIGS. 4 and 5, when an organic polymer film substrate isused, the temperature conditions for the deposition of an ITO coatingmust be lower than those for the case where a glass substrate is used.Therefore, even when general high magnetic field RF superimposed DCsputtering deposition is used, it is not possible to form an ITO coatingwith the same properties as those of an ITO coating formed on a glasssubstrate (a low resistance of 100 Ω/square or less and a specificresistance of 2.0×10⁻⁴ Ω·cm or less).

FIG. 6 shows the relationship between the deposition time index and thesurface resistance index of an ITO coating, which was obtained in-lineusing an R-to-R system in a case where the pre-sputtering step (a) wasperformed and then the forming step (A) was performed. Thepre-sputtering step (a) included pre-evacuating the sputtering system to1.5×10⁻⁴ Pa or less and performing pre-sputtering at a ratio of RF powerto DC power of 0.6 using only sputtering gas such as argon gas (withoutintroducing oxygen). The forming step (A) was performed by high magneticfield RF superimposed DC sputtering deposition under the same conditionsas those for the measurement shown in FIG. 3 (the RF frequency used was13.56 MHz). It will be understood that any RF/DC power ratio in therange for the main deposition process may be used.

As shown in FIG. 6, the coating in the phase ▴1▾ or ▴2▾ has a relativelylow resistance but varies in resistance every moment with impuritycontamination fluctuating significantly because at the early stage ofthe discharge deposition process, water and gases are generated from thetarget surface, the wall in the chamber, the organic polymer filmsubstrate, and the like. The coating in this phase appears to have hightransparency and low resistance but is difficult to crystallize bypost-heating so that lower resistance cannot be obtained. As shown inFIGS. 4 and 5, when pre-sputtering is performed by this phase or whenpre-sputtering is not performed, the resulting coating cannot have thedesired very low resistance.

However, when the pre-sputtering is further continued so that thedischarge deposition process proceeds beyond the phase ▴2▾, water andgenerated gases decrease while the resistance gradually increases, andthe phase ▴3▾ is reached in which there is generated no water or gas.When the pre-sputtering is further continued, the stable phase ▴4▾ isobtained. In the stable phase ▴4▾, not only the coating is notcontaminated with impurities derived from water and generated gases, butalso the resulting coating can have high quality with a smaller amountof introduced oxygen because of the activation of the surface of theindium-based complex oxide target by the RF discharge.

The pre-sputtering (a) was so performed that the phase ▴4▾ (called thestable phase) in FIG. 6 was reached, in which a 28-nm-thick ITO coatingwas formed on a 125-μm-thick PET film using an indium-tin complex oxide(ITO) target with a tin oxide content of 10% by weight, placed in thehigh magnetic field RF superimposed DC sputtering system of an R-to-Rsystem (the intensity of the horizontal magnetic field on the targetsurface was 100 mT). The temperature of the film substrate was 120° C.,and the reached degree of vacuum was 5×10⁻⁵ Pa. Only argon gas wasintroduced, and the deposition pressure was 0.3 Pa.

After the pre-sputtering (a) was so performed that the stable phase ▴4▾in FIG. 6 was reached, a 28-nm-thick ITO coating was continuously formedusing the same target under the same conditions as those in FIG. 5except that oxygen gas was not introduced. Specifically, the ITO coatingwas obtained under the main deposition conditions: a 13.56 MHzhigh-frequency power of 1,000 W, a DC power of 1,000 W, and a ratio ofRF power to DC power of 1. The resulting ITO coating had an initialsurface resistance (R₀) of 62 Ω/square and had a surface resistance(R_(150° C. 1 h)) of 58 Ω/square after annealed at 150° C. for 1 hour.These results show that the pre-sputtering (a) followed by the maindeposition step (A) makes it possible to obtain the desiredlow-resistance coating.

FIGS. 7 to 10 show that the preferred ratio of RF power to DC powervaries with the frequency of the RF power source used in the highmagnetic field RF superimposed DC sputtering deposition. FIG. 7 showsthe behavior in a case where the RF power source frequency is 13.56 MHz.FIG. 7 shows the resistance of an ITO coating obtained by a processincluding: performing the pre-sputtering step (a) at a roll electrodetemperature of 150° C. for deposition and a ratio of RF power to DCpower of 0.6 without introducing oxygen until the stable phase isreached; and then performing the forming step (A) by high magnetic fieldRF superimposed DC sputtering deposition at different ratios of RF powerto DC power without introducing oxygen. The temperature of the rollelectrode for deposition was set at 150° C., and the thickness of theITO coating was 28 nm. Other conditions were the same as those in FIG.6.

FIG. 7 shows that as the ratio of RF power to DC power approaches 1, theresistance of the coating immediately after the deposition decreases,and the degree of oxidation also approaches the level of an appropriatecoating. As the ratio exceeds 1, the coating tends to have too high anoxygen content and to increase in resistance. On the other hand, as thepower ratio decreases, the coating becomes oxygen-deficient andincreases in resistance. It is apparent that when the ratio of RF powerto DC power was 1, a surface resistance of 58 Ω/square and a specificresistance of 1.6×10⁻⁴ Ω·cm were obtained after annealing at 150° C. for1 hour.

FIGS. 8, 9, and 10 show the results obtained when the RF power sourcefrequency was 27.12 MHz, 40.68 MHz, and 54.24 MHz, respectively, in thesame process. The other conditions for the results in FIGS. 8, 9, and 10are the same as those for the results in FIG. 7 except that the ratio ofRF power to DC power was 0.3 in the pre-sputtering step (a). When theratio of RF power to DC power was about 0.35, the surface resistance wasthe lowest with respect to both the initial surface resistance (R₀) ofthe ITO coating immediately after the deposition and the resistance(R_(150° C. 1 h)) after annealing at 150° C. for 1 hour. As the ratio ofRF power to DC power approaches 1, the coating becomes oxygen-excess. Onthe other hand, as the ratio approaches 0, the coating becomesoxygen-deficient. FIG. 10 shows that when the RF power source frequencywas 54.24 MHz, a 28-nm-thick ITO coating with a surface resistance aslow as 57 Ω/square was obtained after annealing at 150° C. for 1 hour.

EXAMPLES

Hereinafter, the invention will be described with reference to examples,which however are not intended to limit the invention. Hereinafter,examples of the invention will be described more specifically.

Example 1 Organic Polymer Film Substrate

The organic polymer film substrate used was a polyethylene terephthalate(PET) film O300E (125 μm in thickness) manufactured by MitsubishiPlastics, Inc.

(Pretreatment)

The PET film was placed in an R-to-R sputtering deposition system sothat an ITO thin coating could be deposited on the smooth surface of thePET film opposite to its lubricated surface. While the film was taken upusing a roll electrode heated at 120° C., degassing was performed withan evacuation system including a cryogenic coil and a turbo-pump, sothat an atmosphere with a degree of vacuum of 3×10⁻⁵ Pa was obtainedwhile the film was fed without deposition. Subsequently, argon gas wasintroduced into the sputtering deposition system, and the PET surfacewas pretreated by allowing the PET film to pass through a plasmadischarge region with an RF power source (13.56 MHz).

(Formation of Undercoat Layer)

An Al₂O₃ thin coating with a thickness of 20 nm was deposited on theplasma-treated surface of the PET film by reactive dual magnetronsputtering from an Al metal target.

(Pre-Sputtering of ITO Target)

Subsequently, while the vacuum was maintained, an ITO oxide target(manufactured by Sumitomo Metal Mining Co., Ltd., 10% by weight in tinoxide content), which was previously set on the electrode of a highmagnetic field RF superimposed DC sputtering deposition system, waspre-sputtered under the conditions of a DC power density of 1.1 W/cm²and a ratio of RF power (13.56 MHz) to DC power of 0.6. The horizontalmagnetic field at the surface of the target was 100 mT. While the filmsubstrate was taken up at a low rate, the pre-sputtering was performedwith the surface resistance and transmittance being measured with anin-line monitor. Other conditions were a film substrate temperature of150° C. and introduction of argon gas only. The pre-sputtering wasperformed at a pressure of 0.32 Pa. The pre-sputtering was performeduntil the resistance monitored in-line reached a stable level.

(Main Sputtering Deposition from ITO Target)

Using the same ITO target as in the pre-sputtering, a 28-nm-thick ITOcoating was deposited by performing a main sputtering process under theconditions of a DC power density of 1.1 W/cm² and a ratio of RF power(13.56 MHz) to DC power of 1 in the same high magnetic field RFsuperimposed DC sputtering deposition system. The horizontal magneticfield at the surface of the target was 100 mT. The temperature of thefilm substrate was 150° C., and only argon gas was introduced. The mainsputtering deposition pressure was 0.32 Pa.

(Annealing)

The ITO-coated PET film was heat-treated at 150° C. for 1 hour in theair to give a transparent conductive film.

Examples 2 to 7 and Comparative Examples 1 to 4

Transparent conductive films were obtained as in Example 1, except thatthe tin oxide (SnO₂) content of the ITO target, the RF power sourcefrequency, the ratio of RF power to DC power, and the amount ofintroduction of oxygen in the high magnetic field RF superimposed DCsputtering deposition, and the annealing temperature were changed asshown in Table 1.

In Example 6, the ITO coating was deposited under the same conditions asthose in Example 1, except that in addition to argon gas introducedduring the main deposition process, oxygen gas was also introduced in anamount of 0.5% relative to the amount of argon and that the depositionwas performed at a film substrate temperature of 170° C. In Example 6,the annealing step (B) was not performed. In Example 7, the ITO coatingwas deposited under the same conditions as those in Example 1, exceptthat the ratio of RF power to DC power was 0.6 and that oxygen gas wasintroduced in an amount of 0.1% relative to the amount of argon.

In Comparative Example 1, common DC magnetron sputtering deposition wasperformed in a high magnetic field of 100 mT, instead of the highmagnetic field RF superimposed DC sputtering deposition.

(Evaluation)

The transparent conductive films obtained in the examples and thecomparative examples were evaluated as described below. Table 1 showsthe results.

(Measurement of Surface Resistance)

The surface resistance of the ITO coating of each transparent conductivefilm was measured with Loresta GP (model MCP-T600) manufactured byMitsubishi Petrochemical Co., Ltd.

(Observation of the Crystalline State of Coating)

The crystalline state of the ITO coating was checked as follows. Onlythe ITO coating was sampled from the transparent conductive film by apeeling method and then observed with a transmission electron microscope(TEM) (Hitachi, HF-2000) at an acceleration voltage of 200 kV. FIG. 12is a TEM photograph showing crystals in the ITO film obtained in Example5 according to the invention.

(Evaluation of Coating Thickness)

The thickness of the ITO coating was measured as follows. The sample wasfixed with resin and then sliced into ultra-thin sections with Hitachi,FB-2100. The sections were observed and measured with the TEM.

(X-Ray Diffraction Measurement)

Grazing incidence X-ray diffraction measurement was performed with theinstrument shown below, and the ratio of the (440) plane peak intensityto the (222) plane peak intensity was determined. FIG. 11 is an X-raydiffraction chart of the ITO film obtained in Example 1 according to theinvention. Powder X-ray diffractometer RINT-2000 manufactured by RigakuCorporation

Light source: Cu-Kα radiation (wavelength: 1.541 Å), 40 kV, 40 mA

Optical system: collimated beam optical system

Divergence slit: 0.05 mm

Receiving slit: 0.05 mm

Monochromation and collimation: using a multilayer bevel mirror

TABLE 1 Forming step (A) Evaluations (RF superimposed DC R₀ aftersputtering deposition) deposition R_(150° C 1 h) after annealing of step(B) ITO coating Amount (%) Annealing of step (A) Peak SnO₂ RF sourceRF/DC of oxygen step (B) Surface Surface Specific intensity Thicknesscontent frequency power relative Temperature resistance resistanceresistance ratio (nm) (wt %) (MHz) ratio to argon (° C.) (Ω/□) (Ω/□) (Ω· cm) (I₄₄₀/I₂₂₂) Example 1 28 10 13.56 1 0 150 254 59.6 1.67 × 10⁻⁴0.17 Example 2 28 10 13.56 0.6 0 150 300 63.2 1.77 × 10⁻⁴ 0.17 Example 328 10 27.12 0.35 0 150 272 59.1 1.65 × 10⁻⁴ 0.19 Example 4 28 10 40.680.35 0 150 263 60 1.68 × 10⁻⁴ 0.16 Example 5 28 12.7 54.24 0.35 0 160210 49 1.37 × 10⁻⁴ 0.19 Example 6 28 10 13.56 1 0.5 None 65 68 1.90 ×10⁻⁴ 0.18 Example 7 28 10 13.56 0.6 0.1 150 240 60 1.68 × 10⁻⁴ 0.17Comparative 28 10 — DC only 1.5 150 324 105 2.94 × 10⁻⁴ 0.25 Example 1Comparative 28 10 13.56 0.2 0.5 150 233 104 2.90 × 10⁻⁴ 0.20 Example 2Comparative 28 10 54.24 0.1 0.5 150 171 114 3.20 × 10⁻⁴ 0.21 Example 3Comparative 28 10 54.24 1 0 150 110 119 3.34 × 10⁻⁴ 0.24 Example 4

The ITO coating with a thickness of 28 nm and a tin oxide content of 10%by weight, obtained in each of Examples 1 to 4, had a low specificresistance of around 1.7×10⁻⁴ Ω·cm. The ITO coating with a thickness of28 nm and a tin oxide content of 12.7% by weight, obtained in Example 5,had a lower specific resistance of 1.37×10⁻⁴ Ω/square. The ITO coatingobtained immediately after the deposition in each of Examples 1 to 5 wasan amorphous coating containing scattered crystalline parts andtherefore vulnerable to an acid etching step. The TEM measurement showedthat the ITO coating obtained after the annealing was completelycrystallized. In Example 6, the ITO coating was already completelycrystallized immediately after the deposition.

The X-ray diffraction analysis also showed that the ITO coating obtainedin each of Examples 1 to 7 had a peak intensity ratio (I₄₄₀/I₂₂₂) ofless than 0.2. Since the resulting ITO coating was completelycrystallized, the results on the reliability against 100° C. heat andthe reliability against 85° C. heat and 85% humidity, necessary forapplications such as touch panels, were also good. Each transparentconductive film (including the PET film substrate) had a transmittanceof about 90% as measured in the air (at a wavelength of 550 nm). Thetransmittance was measured with MCPD-3000 manufactured by OtsukaElectronics Co., Ltd. The transmittance is preferably 85% or more, morepreferably 88% or more.

No oxygen needs to be introduced at almost every RF/DC power ratio.However, a very small amount of oxygen gas may be introduced underconditions around the upper or lower limit of the optimal RF/DC powerratio range at each RF frequency. In Example 6 where the RF/DC powerratio was 1 at 13.56 MHz, the deposition was performed while a verysmall amount of oxygen was introduced in such a way that the amount ofoxygen was 0.5% relative to the amount of argon. Under such conditions,a substantial amount of oxygen is incorporated into the coating, so thata crystallized ITO coating is obtained immediately after the deposition.In this case, the annealing step is unnecessary, and if the coating isheated at 150° C. for 1 hour, a phenomenon is observed in whichpolycrystallization proceeds to reduce mobility so that the resistanceslightly increases.

In Example 7 where the RF/DC power ratio was 0.6 at 13.56 MHz, thedeposition was performed while a very small amount of oxygen wasintroduced in such a way that the amount of oxygen was 0.1% relative tothe amount of argon. Under conditions where the amount of oxygen isclose to 0 relative to the amount of argon, an oxygen-deficient coatingis formed, and therefore, the annealing for improving the transmittanceand reducing the surface resistance tends to take a long time. In such acase, therefore, oxygen should be introduced in an amount of 0.5% orless relative to the amount of argon so that the transmittance can beimproved and the annealing time can be reduced. However, if oxygen isintroduced in an amount more than that amount, the specific resistancewill not significantly decrease so that it will be impossible to obtainthe desired specific resistance.

On the other hand, Comparative Example 1 shows the results of highmagnetic field common magnetron sputtering deposition. A magnetic fieldas high as 100 mT effectively reduces the discharge voltage to 250 V. Ata magnetic field of 30 mT, damage to the deposited coating is reducedaccording to the reduction of the discharge voltage to about 450 V.Therefore, a specific resistance of 2.94×10⁻⁴ Ω·cm is obtained.

Comparative Examples 2 to 4 show the properties of ITO coatings obtainedby performing high magnetic field RF superimposed DC sputteringdeposition under conditions out of the RF/DC power ratio range accordingto the invention at each frequency. According to the results, when theRF/DC power ratio exceeds the upper limit, a coating with too high anoxygen content is formed, which has a high resistance immediately afterthe deposition and also has a higher surface resistance when subjectedto the annealing step. It is suggested that when the RF/DC power ratiois less than the lower limit, the effect of the RF superimposition islow, and the discharge voltage is high, so that damage to the depositedcoating is less effectively reduced and the specific resistance is notsufficiently reduced.

DESCRIPTION OF REFERENCE SIGNS

In the drawings, reference sign 1 represents an organic polymer filmsubstrate, 1A a substrate holder or a can roll, 2 a transparentconductive coating, 2A an indium-based complex oxide target, 3 asputtering electrode, 4 a high magnetic field-generating magnet, 5 amatching box for high frequency introduction, 6 a low-pass filter, 7 ahigh frequency power source (RF power source), and 8 a direct currentpower source (DC power source).

The invention claimed is:
 1. A transparent conductive film, comprising:an organic polymer film substrate; and a transparent conductive coatingprovided on at least one surface of the organic polymer film substrate,wherein the transparent conductive coating is a crystalline coating ofan indium-based complex oxide having a content of a tetravalent metalelement oxide of 7 to 15% by weight as calculated by the formula {(theamount of the tetravalent metal element oxide)/(the amount of thetetravalent metal element oxide+the amount of indium oxide)}×100(%), thetransparent conductive coating has a thickness in the range of 10 nm to40 nm, the transparent conductive coating has a specific resistance of1.3×10⁻⁴ to 2.8×10⁻⁴ Ω

cm, and the transparent conductive coating has main X-ray diffractionpeaks corresponding to (222) and (440) planes and also has a ratio(I₄₄₀/I₂₂₂) of (440) peak intensity (I₄₄₀) to (222) peak intensity(I₂₂₂) of less than 0.2.
 2. The transparent conductive film according toclaim 1, further comprising an undercoat layer provided on the filmsubstrate, wherein the transparent conductive coating is provided on thefilm substrate with the undercoat layer interposed therebetween.
 3. Thetransparent conductive film according to claim 1, wherein theindium-based complex oxide is an indium-tin complex oxide, and thetetravalent metal element oxide is tin oxide.
 4. The transparentconductive film according to claim 1, wherein the peak intensity ratio(I₄₄₀/I₂₂₂) is 0.19 or less.
 5. A method for producing the transparentconductive film according to claim 1, comprising: the step (A) offorming a transparent conductive coating on at least one surface of anorganic polymer film substrate in the presence of inert gas by RFsuperimposed DC sputtering deposition using an indium-based complexoxide target with a high horizontal magnetic field of 85 to 200 mT at asurface of the target, wherein the indium-based complex oxide target hasa content of a tetravalent metal element oxide of 7 to 15% by weight ascalculated by the formula {(the amount of the tetravalent metal elementoxide)/(the amount of the tetravalent metal element oxide+the amount ofindium oxide)}×100(%).
 6. The method for producing the transparentconductive film according to claim 5, wherein in the forming step (A),the high magnetic field RF superimposed DC sputtering deposition isperformed with a ratio of RF power to DC power of 0.4 to 1.2 when an RFpower source has a frequency of 10 to 20 MHz.
 7. The method forproducing the transparent conductive film according to claim 5, whereinin the forming step (A), the high magnetic field RF superimposed DCsputtering deposition is performed with a ratio of RF power to DC powerof 0.2 to 0.6 when an RF power source has a frequency of more than 20MHz to 60 MHz.
 8. The method for producing the transparent conductivefilm according to claim 5, wherein in the high magnetic field RFsuperimposed DC sputtering deposition for the forming step (A), theorganic polymer film substrate has a temperature of 80 to 180° C.
 9. Themethod for producing the transparent conductive film according to claim5, wherein in the forming step (A), the high magnetic field RFsuperimposed DC sputtering deposition is performed without introducingoxygen.
 10. The method for producing the transparent conductive filmaccording to claim 5, wherein in the forming step (A), the high magneticfield RF superimposed DC sputtering deposition is performed while oxygenis introduced in such a way that the amount of oxygen is 0.5% or lessrelative to the amount of the inert gas.
 11. The method for producingthe transparent conductive film according to claim 5, further comprisinga pre-sputtering step (a) that is performed before the high magneticfield RF superimposed DC sputtering deposition and comprises forming acoating in the presence of inert gas without introduction of oxygen byRF superimposed DC sputtering deposition with a ratio of RF power to DCpower of 0.4 to 1.2 at an RF power source frequency of 10 to 20 MHzuntil a resulting resistance reaches a stable level.
 12. The method forproducing the transparent conductive film according to claim 5, furthercomprising a pre-sputtering step (a) that is performed before the highmagnetic field RF superimposed DC sputtering deposition and comprisesforming a coating in the presence of inert gas without introduction ofoxygen by RF superimposed DC sputtering deposition with a ratio of RFpower to DC power of 0.2 to 0.6 at an RF power source frequency of morethan 20 MHz to 60 MHz until a resulting resistance reaches a stablelevel.
 13. The method for producing the transparent conductive filmaccording to claim 5, further comprising an annealing step (B) that isperformed after the forming step (A).
 14. The method for producing thetransparent conductive film according to claim 13, wherein the annealingstep (B) is performed at a temperature of 120 to 180° C. for 5 minutesto 5 hours in the air.